Engine performance may be increased by disabling exhaust gas communication between cylinders. This may be accomplished by an exhaust manifold comprising individual exhaust tubes (e.g., exhaust runners) for each cylinder. The exhaust runners remain separated, and therefore the exhaust gas remains separated before coming together at a collector. A longer separation can minimize exhaust pulse overlap and enable optimized valve timing.
However, exhaust runners are often longer with significant mass away from the engine in a cantilever configuration. Thus, the longer exhaust runners are prone to higher stress through a bending moment than other manifolds (e.g., cast iron log style exhaust manifolds). The higher stress increases a likelihood of degradation (e.g., single overload or fatigue cracking) at a junction between the exhaust runner and an inlet flange coupling the runner to the engine.
Other attempts to address stress in long exhaust runners include casting cores and adding brackets. Stress can also be managed through a welding geometry. One example approach is shown by Roussel et al. in U.S. Pat. No. 4,832,383. Therein, exhaust runners are welded to a flange of an engine in a circumferential direction via a chamfered weld. The weld allows the exhaust runner to more accurately fit into the inlet flange.
However, the inventors herein have recognized potential issues with such systems. As one example, the weld is unable to flex and/or bend under high engine vibration energy. Thus, the exhaust runner(s) are still prone to high stress generated via combustion and may result in a fatigue failure at the welded joint.
In one example, the issues described above may be addressed by a method for a runner having a runner wall interfacing with an inlet flange of a cylinder head and a collar positioned at the interface forming an annular air gap around an exterior of the runner. In this way, the collar may be able to flex in response to stresses generated by operating a vehicle and be less susceptible to a fatigue fracture and thus increase a longevity of the exhaust runner.
As one example, the collar is formed with a single wall extending from the inlet flange to the exhaust runner at respective positions spaced away from a corner of the interface. A geometry of the collar (e.g., L-shaped, I-shaped, square cross-section, and triangular cross-section) may increase stress load sharing via a spring-like flexibility of the collar. The air gap is interruptedly sealed at the respective positions via weld beads such that there are openings leading to the air gap from the engine or an ambient atmosphere. The air gap extends uninterruptedly fully around an outer circumference of the outer surface of the runner wall in one example. It will be appreciated by someone skilled in the art that the air gap may also be segmented (e.g., interrupted) according to a shape of the collar. In one embodiment, the collar may be welded to only a single runner of a plurality of runners in order to manage the stress across the runners. The single runner may be the shortest runner of the plurality of runners or a runner closest to a rear of a vehicle. Additionally or alternatively, the single runner may comprise a most acute bend or highest cantilever of the plurality of runners. In this way, the single runner, without the collar, may have a greatest likelihood of degradation compared to the plurality of runners. By welding the collar to the single runner, the collar may distribute a stress load received by the single runner such that the likelihood of degradation for the single runner is decreased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.